1. Field of the Invention
The present invention relates generally to a medical apparatus used during the performance of eye surgery and in particular, is directed towards a positioning assembly for retaining and positioning a patient's eye for cutting of the cornea during a surgical procedure, such as to correct for refractive error. More specifically, the present invention is specifically directed to achieving and maintaining an improved attachment of a positioning segment to the eyeball during surgery.
2. Description of the Related Art
The eye works on a principle very similar to that of a camera wherein the iris, or colored portion of the eye about the pupil, functions like a shutter to regulate the amount of light admitted to the interior of the eye. The cornea or clear window of the eye, and the lens, which is located behind the pupil, serve to focus the light rays from an object being viewed onto the retina at the back of the eye. The retina then transmits the image of the object viewed to the brain via the optic nerve. Normally, these light rays will be focused exactly on the retina, which permits the distant object to be seen distinctly and clearly. Deviations from the normal shape of the corneal surface however, produce errors of refraction in the visual process so that the eye becomes unable to focus the image of the distant object on the retina, with the result that one sees a blurred image.
About twenty years ago, such refractive errors could only be treated with eyeglasses or contact lens, both of which have well known disadvantages for the user. Since then, however, surgical operations have been developed to change the refractive condition of the eye. Several methods and special instruments have been designed for performing this kind of surgery, which are primarily directed to reshape the cornea. It will be appreciated that the goal of corneal reshaping is to modify the curvature of the cornea, i.e., either to flatten or increase its curvature depending on the patient's condition, so that light rays passing through the cornea will thereafter be refracted to focus or converge directly onto the retina, thereby permitting the patient to view a distant object clearly.
One such surgical operation is keratomileusis, which requires a precise reshaping of the cornea by cutting and separating a thin layer of corneal tissue, termed the corneal cap, by lathing that tissue and then, by suturing the reshaped corneal tissue back into place on the eye. Keratomileusis is viewed, however, as having several drawbacks, and consequently, has been abandoned in recent years. Automated Lamellar Keratectomy (ALK) is another surgical technique which developed as an outgrowth of keratomileusis. In an ALK procedure, the eye is typically first numbed by a drop of anesthetic, and then, a device having a ring shaped configuration is placed on the eye to carefully position the cornea (termed "centration" in the art) for being cut by a very fine microsurgical instrument known as a microkeratome. The microkeratome is generally a blade carrying device that must be manually pushed or mechanically driven in a cutting path across the ring shaped device to cut into the cornea. Under an ALK procedure to treat near-sightedness, the microkeratome is typically first used to cut and lift a thin layer of the cornea, instead of severing it, and second, to carry out a reshaping of the cornea by way of a second pass of the microkeratome over the cornea with the cutting element adjusted to pass therethrough at a desired and pre-determined corrective depth. Thereupon the thin, raised layer of corneal tissue is put back in place over the cornea for healing. Despite developments in the art utilizing a laser to carry out the step of re-shaping the cornea, the above-described ALK procedure for near-sightedness may still be followed in certain cases, depending on the depth of the corneal cut needed. Conversely, ALK procedures to treat far-sightedness, wherein the microkeratome is used to make a single cut, are generally no longer followed given the advances which have since occurred in the field.
From the foregoing, it will be appreciated that ALK procedures are considered to possess drawbacks, particularly in that the penetration of the microkeratome's cutting element into the cornea to a precise depth is critical and may not always be achieved. Thus, in more recent years, substantial advances have been made for correcting refractive errors of the eye utilizing a laser to reshape the cornea. One such procedure, known as Laser Intrastromal Keratomileusis, (LASIK), is currently considered optimal because it allows sculpting of the cornea without damaging adjacent tissues, and further, because with the aid of computers, the laser can be programmed by a surgeon to more precisely control the amount of tissue removed, and significantly, to permit more options for the reshaping of the cornea. Under LASIK procedures, the eye is still typically positioned within a ring shaped device and a microkeratome is typically first used to cut into the cornea so as to raise a thin layer of the cornea, prior to treatment with the laser to reshape the cornea. Still, however, and regardless of the procedure employed, great care and precision are of critical importance to the safety and success of the procedure.
The use of a device having a ring shaped configuration to hold the eyeball in place during a corneal reshaping surgery is well known in the art. Such devices are commonly attached to the eyeball temporarily by way of a suctioning force or vacuum. A typical suction ring device is depicted in FIG. 1 and is seen to include an annular, hollow ring, R, defining an aperture, A, which allows the cornea to be exposed, and an open bottom side that is applied to the surface of the eyeball around the cornea. The ring, R is seen to be in communication with a hollow suction tube, T which opens into the hollow open bottom side of the ring. Commonly known suction ring devices apply a vacuum to the ring R, via tube T, to the eyeball at a single point, P, illustrated in FIG. 2. When the suction ring is applied to the eyeball, with suction or a vacuum applied to the hollow tube, and thus, to the bottom of the ring, the suction ring attaches to the surface of the eyeball surrounding the cornea, with the suction force holding the ring in a reasonably secure fashion, to the eyeball. As a result, the suction ring has become a conventional device in ophthalmic practice, and it should be noted, is designed to be re-usable so as to accommodate a large number of patients over the course of its useful life.
Ophthalmologists have complained, however, that during surgery the vacuum seal, which attaches the suction ring device to the eyeball, may break on occasion. Although not a common occurrence, when the vacuum seal breaks, it is extremely serious in that the precise positioning or centration of the suction ring on the eyeball is lost. More specifically, a critical first step in performing corneal reshaping surgery is the accurate centration of the suction ring on the eye, in precise alignment with the optical axis, with the suctioning force applied to achieve a reliable vacuum seal to maintain the eyeball in the centrated position. If surgery on the eye is underway, with reshaping of the cornea in progress, and the vacuum seal breaks, there can be devastating consequences. Consequently, it is considered imperative that any cutting of the cornea be stopped immediately. Moreover, surgery on the eye should not resume as quite obviously, it is not feasible for the suction ring to be precisely re-aligned or re-centrated in its original position, and it is even more improbable that the cutting element can be precisely re-aligned with the cutting of the cornea already underway. Surgery in progress should therefore be stopped, and any cut portions of the cornea should be returned to a proper position on the eye, with the eye being permitted to heal over the course of three months, before surgery on that eye can be undertaken anew. It will therefore be appreciated that this situation is utterly undesirable for several reasons, but primarily because of the potentially devastating consequences to the patient.
One known factor which contributes to the occasional breakage of the vacuum seal attaching the suction ring to the eyeball is the partial or complete occlusion of the suction force being applied. Specifically, when a vacuum is applied to known suction ring devices during surgery, the vacuum necessarily acts on tissue about the eyeball and more particularly, a mucous membrane that lines the exposed surface of the eyeball known as conjunctiva. With many patients, this factor does not affect the surgery. Other patients, however, have a condition is generally known in the art as "chemosis" which can affect the surgery. Chemosis is a condition wherein fluids can exist under the conjunctiva of the eye such that during surgery, the action of the vacuum on the conjunctiva can cause it to pull away from the surface of the eyeball and towards the single vacuum focal point P of the suction ring. When this occurs, the vacuum can become completely or partially blocked, with the result that the vacuum seal is compromised and likely, broken. It will be recognized that the patient condition of chemosis is relatively uncommon and generally, will be detected before cutting of the cornea begins, and in that case, there is no untoward consequence for the patient. The concern for serious complications arises when surgical cutting of the cornea is underway at the time the vacuum seal breaks, such as by the effects of chemosis, explained above.
Another factor may also contribute to the occasional breakage of the vacuum seal which attaches the suction ring to the eyeball during surgery. Specifically, during surgery the action of the suction force may draw some mucus from the eye into the internal passages of the vacuum, such as into the hollow tube T, shown in FIGS. 1 and 2. Should this occur, it is unlikely to lead immediately to the occlusion of the vacuum. On the other hand, an effective cleaning of the suction ring's internal vacuum passages is tedious at best, and at worst, may not truly be possible. Consequently, any mucus which is drawn into the vacuum passages of the suction ring may remain there to harden in place. Over time then, it is possible for mucus to build-up and accumulate within the internal vacuum passages of a suction ring. A partial or complete occlusion of the suction force applied to the suction ring might eventually result during a subsequent surgery, and lead to a breakage of the vacuum seal.
A potential solution to the problem might be to apply the vacuum to known suction ring devices at more than a single vacuum point on the suction ring. However, the action of a suction force applied to the suction ring, even through a plurality of vacuum points thereabout, might still cause chemosis in that conjunctiva could still block one or more of the vacuum points. This is particularly true in that the suction force applied to the suction ring would likely remain un-dispersed and concentrated at the vacuum points. Additionally, the problem would persist of eye mucus becoming lodged within the interior vacuum passages of the suction ring. As has been described, a thorough cleaning of the suction ring's internal vacuum passages may not be possible, and even if it were possible, cleaning mucus out of the internal vacuum passages would be time consuming. This factor alone carries a negative economic impact in that only a smaller number of surgeries could be performed with the device in a single day.
Therefore, there remains a need in the art for a positioning assembly which not only retains and positions a cornea of patient's eye during surgery, but which has an improved ability to remain securely attached to the eyeball during surgery, without occlusion of the vacuum. Any such improved positioning assembly should be capable of functioning with known suction rings. It would be highly beneficial if any such improved positioning assembly were able to enhance the suction gripping ability of the suction ring device so as to offer a seal about the eye which is more resistant to being broken during surgery. Any such suction enhancement assembly would preferably provide a suction force substantially about the girth of the eyeball, if not entirely thereabout, instead of to a single point adjacent the eyeball, and further, would be structured to apply the suction force about the eyeball in a dispersed and uniform manner. Any such suction enhancement assembly would ideally prevent the effects of chemosis, that is, prevent conjunctiva from partially or completely blocking the suctioning force applied to the suction ring, and further, would ideally limit, if not prevent altogether, eye mucus from entering the interior vacuum passages of the suction ring during surgery.